Automotive vehicles with coordinated front and rear wheel steering systems are known. In modern applications, such steering systems may be used, e.g., in relatively large sport utility vehicles or trucks. The operator retains control over the steering of the vehicle's front wheels, and a vehicle computer-based system controls steering of the rear wheels. For example, one rear wheel steering system includes an electric motor-driven, rack and pinion rear-wheel-steer actuator that, upon computer command, produces a desired rear-wheel-steer angle to enhance the handling and maneuverability of the vehicle.
When the steerable rear wheels are set at an angle to the same side of the longitudinal axis of the vehicles as the front wheels, the system is considered to be providing "in-phase" rear wheel steering. "Out-of-phase" steering, conversely, is where the rear wheels are disposed to the opposite side of the vehicle longitudinal axis from the front wheels. Out-of-phase rear wheel steering markedly shortens the turning radius of a large vehicle. The on-board steering controller determines the rear-wheel-steer angle as a function of vehicle speed and the operator hand steering-wheel angle. The system, in general, will provide an out-of-phase steering angle at low vehicle speed to reduce the turning radius of a vehicle and in-phase steering at high vehicle speed to enhance directional stability.
The steering controller, thus, continually monitors vehicle speed, forward or reverse, and the angles, right or left, of the steered wheels with respect to the longitudinal axis of the vehicle. The controller also determines the yaw rate (i.e., the turning motion) of the vehicle in setting the steering angle of the rear wheels. While the front wheels may be steered at angles, e.g., from +33.degree. (left) to -33.degree. (right) with respect to the vehicle axis, the steering range of the rear wheels is usually smaller, e.g., from +12.degree. to -12.degree.. In steering the front wheels, the operator typically can rotate the hand wheel up to about 540.degree. in either direction from its wheel centered position.
Larger automotive vehicles are often used to pull trailers, and sometimes it is necessary for the operator to back up the vehicle-trailer combination. Backing-up a front wheel steering vehicle is now within the experience and skill of vehicle operators who need to perform such jobs. But performing the same task with a vehicle-trailer combination is counterintuitive and not within common experience. It is an object of this invention to provide a computer-based, driver-interactive process to assist in backing-up a vehicle-trailer combination with the aid of rear wheel steering.